Recent Technological Developments

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Recent Technological Developments

• Tissue Harmonics
• Spatial Compounding
• Extended Field of View Imaging
• 3D 4D Imaging

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These new technologies are reviewed in excellent
detail in the 4th Ed of HedrickPages 140 - 152
Make sure you read it!
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Harmonic Imaging
-Be Careful!!! The term Harmonic Imaging is used
to describe two separate modes of imaging. 1.
Associated with contrast agents use. 2. Tissue
harmonics.
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Harmonic Imaging Associated with Contrast Agents
- U/S Contrast Agents generally consist of
encapsulated microbubbles that boost the
echogenicity of the blood and perfused tissues.
More importantly resonance phenomena within the
microbubbles give rise to harmonic frequencies
which can be selectively received.
3 MHz
3 MHz
6 MHz
6 MHz
Microbubble
3 MHz
RBC
3 MHz
If you tune the receiver to receive at twice the
transmitted frequency then the harmonic echoes
from the microbubbles will dominate the returning
signal.
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The history of Tissue Harmonics

• The fact that harmonics frequencies arise from
  soft tissue even without the injection of
  microbubble contrast agents was discovered by
  mistake!
• Researchers working on the development of
  ultrasound contrast agents found that an image of
  the tissues would still be produced when the
  receiver was tuned to receive at twice the
  transmitted frequency. In fact some of the
  features of the image were superior to the
  fundamental image.
• From there they had to set about explaining why
  these natural tissue harmonics occurred!

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Tissue Harmonic Processing
Acoustic field
Transmitted signal
After Processing
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Tissue Harmonics- The Basics

• Wave travels faster in compressive phase (NB
  Increased particle density) and slower during
  rarefaction.
• This Nonlinear Propagation shifts a portion of
  the beams energy to harmonic frequencies.
• Harmonics are not produced in the first few cm of
  tissue.
• Harmonics are most prominent in the central
  portion of the transmitted beam. Therefore
  lateral resolution is typically superior in
  harmonic mode.
• Most Harmonic Energy is in the Second Harmonic.
  This has a frequency which is twice the
  fundamental frequency.

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From 4th Ed of Hedrick
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Pros And Cons of Harmonics

• Pros
• Many Fundamental Image artefacts are reduced
• Side Grating Lobes
• Reverberation
• gtgt Better Contrast Resolution due to less
  noise.
• Better Lateral Resolution.
• Cons
• Less Penetration

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Fundamental Image
Harmonic Image
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Spatial Compounding

• Basics- Angle of incidence to an interface
  influences the amplitude of the echo returning.
  If you produce an image with transmitted beams at
  multiple angles then border definition will
  improve.
• Most of the major ultrasound equipment companies
  have adopted this technique. It is given
  different proprietary names such as SonoCT.
• Beam steering principles are employed to steer
  beams at multiple angles through the FOV. The
  data stored at each pixel is the average of the
  multiple angles.
• As well of better border definition there is
  noise reduction achieved because of the data
  averaging at each point.
• As the technique is performed in real time there
  is no effect on frame rate. Just like frame
  averaging has no effect on FR, except in this
  case the previous frames are taken from different
  beam steering angles.

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From 4th Ed of Hedrick
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Spatial Compounding Clinical Cases
Spatial Compound Image
Note reduced artefact in the anechoic renal cysts
Standard Image
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Spatial Compound Image
Note greater continuity in appearance of muscle
fibres and more defined margins to the partial
tear of this supraspinatus tendon.
Standard Image
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Extended Field of View Imaging
Normal Calf Muscles
This technique can produce FOVs over 500mm wide
(a big improvement from the 40mm offered by the
average linear array transducer). It is
particularly useful for demonstrating MSK anatomy
and pathology.
Large Calf Muscle Tear
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Extended Field of View Imaging

• Different Proprietary names exist for this
  technique Siescape, Panoramic Imaging, Logiqview.
  
• Successive frames are combined to produce the
  extended FOV.
• Computer analysis of successive frames for common
  image features is employed to determine the
  degree of transducer movement between frames.
• Careful and smooth transducer movement in a
  single plane (and lots of practice) is required
  to avoid image artefacts caused by rapid movement.

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3D 4D Imaging

• In 3D imaging a volume of data is scanned and
  displayed as a static image.
• In 4D imaging the volume is scanned in real
  time such that a moving 3D image of the volume
  is shown.

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3D 4D Basics
By moving the Transducer perpendicular to the
scan plane it is possible to produce a volume of
ultrasound data. Loaf of Bread Analogy. This
data can be used to create a 3D image or
reconstruct a 2D image not in the original scan
plane.
If the volume of data is reproduced many times a
second. i.e. By having the transducer
mechanically steering through the volume, then a
real time 3D image or 4D image can be created.
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Stilled 4D Images I have produced of two Facial
Clefts of different severity. There is a
counseling benefit in the parents better
understanding the severity of the cleft with the
4D image.
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The non-medical use of 4D ultrasound in pregnancy
is causing much ethical debate in the profession.